1. Field of the Invention
The invention relates to a mold structure and a bumper.
2. Description of the Related Art
Resin molded objects for vehicles, such as automobiles or the like, for example, bumpers or the like, are designed on the basis of a demand for high-quality vehicle body design in recent years, and hence may include undercut portions that extend in a direction that intersects with the release direction of a mold used to mold the molded object.
In addition to a fixed mold and a movable mold that are opened/closed vertically, a mold for molding a molded object having such an undercut portion may have a slide mold for molding the undercut portion and sliding in a direction intersecting with a mold opening direction to allow the molded object to be drawn out when the fixed mold and the movable mold are opened vertically. Due to the structure of the above mold, an protruding parting line (P/L=a mold parting line) is formed on the obverse surface of the molded object corresponding to, for example, the land between the fixed mold and the slide mold (a parting region of the mold).
A mold structure that prevents a parting line from appearing on the design surface of a bumper is described in, for example, Japanese Patent Application Publication No. 2003-205536 (JP-A-2003-205536).
That is, a mold structure that prevents a parting line from being formed on an outer surface of a bumper is described in Japanese Patent Application Publication No. 2003-205536 (JP-A-2003-205536). In the mold structure described in JP-A-2003-205536, the land between the mold and the slide mold is located on an outer surface of the flange portion of an injection-molded object. Specifically, the land between the mold and the slide mold is provided at a position that does not interfere with the exterior appearance. Therefore, the parting line does not appear in the vicinity of the flange portion exposed to the outside.
Furthermore, if the parting line appears on an exterior surface of the molded object, the molded object may be made aesthetically attractive by covering the parting line with another member to conceal it. For example, in Japanese Patent Application Publication No. 2004-196122 (JP-A-2004-196122), a structure is provided with a shade (a concealing member) to make the end of a front bumper invisible from a radiator grill.
A front bumper (see FIGS. 8A and 8B) having “horn portions” that protrude upward from the main body of the bumper to cover a space between a headlamp portion and an upper grill portion and a mold structure for molding the horn portions will be described in a view from a spot in front of a vehicle, as an example of the conventional approach to molding molded object that includes an undercut portion.
When the front bumper having the horn portions shown in FIGS. 8A and 8B is assembled with the vehicle, the assembly is carried out such that a tip of each of the horn portions is interposed between a radiator support and an upper grill as shown in FIG. 9. Further, the mold used in molding each of the horn portions of the bumper employs a slide core because a fastening hole (a through-hole) for assembly, which is formed by being opened through the tip of each of the horn portions, assumes an undercut shape as shown in FIG. 12.
In a mold structure employing such a slide core, a gap may be formed between the slide core and a fixed mold (at a parting position P shown in FIG. 11) due to a mold working error, displacement of the slide core resulting from an injection molding pressure, the creation of a clearance resulting from aging, etc.
The gap is formed because the surface of the molded object is molded using the fixed mold and the slide core which are split (separated) from each other, and the shape of a product or the mold structure does not make it possible to absorb a step resulting from the clearance created due to displacement or aging. In molding according to the mold structure thus having the fixed mold and the slide core, if a parting line as shown in FIG. 10 is noticeable (protruding linearly) and set at a visible position on the obverse surface of the molded object corresponding to the parting position P between the fixed mold and the slide core due to the aforementioned gap, the parting line is visible, for example, at a position shown in FIG. 9 or FIG. 13 at an end of each of the horn portions. As a result, a deterioration in aesthetic attractiveness may be caused when the front hood (bonnet) is open.
Thus, to manufacture a mold, in which the error/displacement during the working of the mold is minimized so that the parting line is less noticeable, a common polish operation for the slide core and the fixed mold for polishing a common polish portion as a peripheral portion of the parting position P between the fixed mold and the slide core shown in FIG. 11 is required. Consequently, the time required for maintenance and the cost of the mold have increased. It should be noted that if a gap is formed at the parting position P between the fixed mold and the slide core due to the aging of the mold, it is necessary to perform operations of “welding (deposit welding) a movable mold”→“mating the movable mold and the slide core with each other”→“commonly polishing the fixed mold and the slide core”.
Thus, the technical elements in JP-A-2003-205536 and Japanese Patent Application Publication No. 2004-196122 (JP-A-2004-196122) may be applied to render the parting line on the molded object less noticeable. However, if art described in Japanese Patent Application Publication No. 2003-205536 (JP-A-2003-205536) is applied, the structural complexity of mold increases in the cost of the mold and a deterioration in the maintainability of the mold. In addition, because the bumper assumes a large variety of shapes in recent years, the parting line may not always be removable from a design surface when the bumper assumes a certain shape. Further, if the art described in Japanese Patent Application Publication No. 2004-196122 (JP-A-2004-196122) is applied, although the parting line may be concealed using a concealment member (a blinder member), the use of a concealment member increases the number of parts used, and accordingly, the production cost of the vehicle.